Generally, capacitors used in a semiconductor device can be categorized as either a poly insulator poly (PIP) capacitor or a metal/insulator/metal (MIM) capacitor, based on its structure. Each of these types of capacitors has peculiar properties and is appropriate selected and used based on the properties of an associated semiconductor device. For example, the MIM structure capacitor may be used in a semiconductor device operating at high frequencies.
In a PIP structure capacitor, a top electrode and a bottom electrode may be formed of conductive polysilicon. Therefore, an oxidation reaction can occur between the top electrode and bottom electrode, and an insulator thin film interface, causing a problem that the capacitance of the capacitor may be reduced. In contrast, the MIM structure capacitor has small resistivity and no parasitic capacitance due to internal depletion, making its possible capacity potentially greater. In other words, a high frequency semiconductor device may use a MIM structure capacitor with metal having good electrical properties in order to prevent the operation of the device from being affected by an undesired RC delay.